The present invention relates to the vacuum art and practice of dehydrating and puffing fruits and vegetables, and in particular to the use of heated edible oils as a liquid heat transfer agent to effect rapid evaporation of natural moisture of the comestible in a vacuum environment. In the past, much land labor has been required, and volume of output has been small. The present invention is addressed to automation and the production of large quantities of output of puffed, crisp product of high quality. The manufacture of the first samples of such comestibles is described in my U.S. Pat. Nos. 2,283,302; 2,110,184; 4,006,260; and 4,556,376. The latter patent claims a system for automation.
In this art, the comestible is enclosed in a vacuum vessel in which the absolute pressure is reduced to only a few millimeters of mercury measure or torr. Then heated edible oil is made to contact the comestible without causing caramelization of the natural sugars or deleterious change of flavor or color. The oil is circulated through a heater and returned to act as a heat transfer liquid overcoming the latent heat of evaporation of the natural moisture. When the moisture content has been reduced to about 2%, the oil is cooled and this cools and hardens the fruit and fixes the puffed structure that has resulted from rapid evaporation. Then the cool oil is drained away. Centrifugal action may be used to assist drainage. The deoiled fruit is returned to normal atmosphere without collapsing the newly generated pores.
An object of the present invention is to provide an automatic system that is capable of very high yield rates of puffed, crisp apple slices, pineapple slices, banana slices, onion slices, and especially of puffed grapes and of puffed raisins, and of other sliced or whole fruits and vegetables as may be suited for the system herein described.
Another object is to provide a true continuous process in which the fresh comestible is inserted as a conveyor-borne stream into the vacuum treater, and is recovered as a stream of finished product ready for packaging, at high yield rate.
Another object is to provide a system that continuously delivers large quantities of high quality product.
The present invention is essentially one of flotation in the vacuum environment. For those comestibles that must be substantially dehydrated before puffing occurs sufficient to make them buoyant such as fresh grapes, apple chunks, pineapple chunks, banana slices, and the like, I provide an initial Stage A. This is a continuous vacuum chamber with a scroll that moves along the sinking comestibles until they have become sufficiently dehydrated by the oil they are in contact with, to become buoyant and to float in this oil. Then the floating comestibles are transferred through a rotary trap into the interior of a second Stage B that provides finishing dehydration down to less than 2% moisture content. The dehydrated comestibles are then cooled and continuously removed from the vacuum chamber, ready for packaging. Dwell time in Stage A is less than an hour; in Stage B, the comestible stays one or two hours.
For those comestibles that will float almost instantly upon being injected into a vacuum environment, especially commercially dried fruit containing 15-25% moisture, I warm them up in vegetable oil to about 85.degree. C. and inject them into my Stage B without preliminary treatment in Stage A.
Hence in the following description, Stage B apparatus is described as being either related to Stage A, or independent of Stage A, depending on circumstances.
I make efficient use of space in my vacuum chambers by mounting trays one over the other. Thus, in my Giant Raisin Puffer, I mount as many as 17 trays one over the other in a large lettuce vacuum cooling chamber, and get as much as 6 or more tons per hour of high quality puffed raisins yield in continuous output rate.
Some fruits and vegetables, when thinly sliced are very delicate, and do not withstand manipulation in a machine without breaking up. examples are: thin apple slices, thin onion, strings, pineapple cross-cuts and the like, where the cuts are across the axis of the fruit, and are large and of 3/16 inch thickness and thinner. After these fruit cuts are dehydrated partially and puffed, they are finished dehydrated in a Stage B apparatus where they remain on one tray 115 until ready for discharge, and thus manipulation and the risk of breaking large, thin slices is minimized. Such Stage B apparatus is illustrated in FIGS. 3, 4, 5 and 6. On the other hand, thicker chunks, more than 3/16 inch thick are successfully dehydrated and recovered unbroken even when the Stage B apparatus moves them repeatedly from a higher level to a lower level, as in the procedures followed in the apparatus of FIGS. 7, 8, 9, 10 where an impeller is used. Raisins and fresh grapes are examples of fruits that will withstand much manipulation without damage.